Synthetic fuel log and method of manufacture



Jan. 10, 1967 EYRE, JR 3,297,419

SYNTHETIC FUEL LOG AND METHOD OF MANUFACTURE Filed Aug. 17, 1965 Swdus Binder Wax Z7 Pu! var/ i175 Hvaiqg l2 Mix/n3 Formation of Lag F I g. I

INVENTOR. Edward E. Eyre, J1: BY

Attorneys United States Patent Ofifice Patented Jan. 10, 1967 3,297,419 SYNTHETIC FUEL LOG AND METHOD OF MANUFACTURE Edward E. Eyre, Jr., Atherton, Calif, assignor to Fyr Tech Products, Inc., San Francisco, Calif., a corporation of California Filed Aug. 17, 1965, Ser. No. 480,423

14 Claims. (Cl. 44-6) This application is a continuation-in-part of my copending application Serial No. 299,760, filed August 5, 1963 now Patent No. 3,240,573.

This invention relates generally to a synthetic fuel log, and to the method or process for the manufacture of the same.

In the manufacture of synthetic fuel logs, two fundamental problems are raised. First, the ignition of the log must be such that it will burn slowly, evenly and with the characteristics of natural logs. Second, the log must be held together both at low temperatures and at high temperatures during burning so that it will not crumble or fall apart into unburned ashes.

There have been numerous attempts to manufacture synthetic fuel logs. However, up to the present time, such synthetic fuel logs have lacked many desirable characteristics. Thus, some logs have been made with fuels which ignite well at low temperatures to initially start the log to burn, but which fail to adequately sustain the log throughout a period of several hours. The fuels which are effective with i-gniters for starting natural logs or other long burning materials are not effective in synthetic fuel logs, in many instances.

Related to the ignition problem is the problem of maintaining the log in the elongate form resembling natural logs. Where the log has been bound together so well that it did not break apart during burning, it was not generally self-igniting or capable of initially burning without great effort and added igniters or other materials. On the other hand, where the log in the past was more easily ignited by the vaporization of the fuel therein, the log tended to break apart after partial burning. To keep the log from breaking apart, past efforts have included wrapping the log with a fiame retardant sheath. However, the sheath adversely affected the burning rate of the log and, moreover, unduly complicated and increased the cost of manufacturing the log. In addition, past efforts at making synthetic fuel logs have included fuels which not only gave off bad odors but, under certain circumstances, would ignite explosively with great danger. There is, therefore, a need for a new and improved synthetic fuel log together with a new and improved method for the manufacture of the same.

In general, it is an object of the present invention to provide a synthetic fuel log which can be readily and economically manufactured.

Another object of the invention is to provide a synthetic fuel log of the above character which is largely formed of a flame-supporting fuel, a combustible fibrous substrate, a low temperature binder and a high temperature binder.

Another object of the invention is to provide a synthetic fuel log of the above character which is covered with an oil-resistant covering.

Another object of the invention is to provide a synthetic fuel log of the above character in which the fuel log will remain reasonably intact during burning and can be turned over with a poker or other fireplace tool without breaking apart.

Another object of the invention is to provide a synthetic fuel log of the above character which ignites rapidly and which will burn evenly and briskly for a relatively long period of time.

Another object of the invention is to provide a synthetic fuel log of the above character which, during burning, will give 013? a substantially uniform flame which virtually surrounds the log.

Another object of the invention is to provide a synthetic fuel log of the above character which will burn without objectionable odor or smoke.

Another object of the invention is to provide a method by which the synthetic fuel logs can be readily formed.

Another object of the invention is to provide a method of the above character for the manufacture of a synthetic fuel log in which the log is extruded directly into an oil-resistant cover.

Additional objects and features of the invention will appear from the following description in which the preferred embodiment is set forth in detail in conjunction with the accompanying drawings.

Referring to the drawings:

FIGURE 1 is a flow sheet illustrating one procedure for carrying out the present invention.

FIGURE 2 is a side elevational view of apparatus incorporating my invention for manufacturing synthetic fuel logs in accordance with the procedure shown in FIG- URE 1.

FIGURE 3 is an isometric view of a synthetic fuel log made in accordance with the present invention.

The present invention involves the production of a synthetic fuel log from a flame-supporting material which is solid at room temperature. A filler or extender of a combustible type is combined with the flame-supporting material. The flame-supporting material and the extender are combined with a binder to provide an elongate synthetic fuel log which will remain intact during burning.

Referring first to the simplified flow diagram shown in FIGURE 1, the flame-supporting material which can be in the form of a wax is headed as shown in step 11. It is then combined in a mixing operation 12 with a filler or extender such as sawdust. The sawdust can first be pulverized in step 13 to provide a filler or extender which is substantially uniform in size. The filler can also be dried in step 13 to stabilize to a standard level of moisture within. This will increase the fillers ability to absorb the wax and will improve the logs initial kindling and eventual combustibility. A high temperature binder is also supplied in the mixing step. After the materials have all been properly intermixed in the mixing step 12, the mixture can be formed into logs as indicated by the step 14 by preferably compacting the mixture into the desired shape by the utilization of pressure. Thereafter, the shaped log is allowed to cool and solidify into a mass which will remain cohesive at room temperature and which will remain reasonably intact while burning.

A machine or apparatus suitable for forming synthetic fuel logs from the ingredients or materials indicated in FIGURE 1 is shown in FIGURE 2. This apparatus consists of a conventional type Marion mixer 21 such as that manufactured by Rapids Machinery Co. Inc. mounted on a conventional type tank scale 2111 such as that manufactured by Howe Richardson Scale Co. The mixing and weighing apparatus 21 is provided with a discharge hopper 22 which supplies the mixed product to a packer 23 which forms the synthetic fuel logs in bags. The bags are supplied to a moving conveyor 24, after which they are moved to a sealing or closing station (not shown).

The apparatus also consists of a large storage hopper 26 which is utilized for storing a supply of a suitable filler or extender such as sawdust which is supplied to the hopper through a supply pipe 27. The hopper is provided with a discharge gate 28 so that a controlled amount of the sawdust or other material carried within the hopper 26 can be supplied to the mixing and weighing apparatus 21. A heated tank 29 contains a suitable flame-supporting material such as wax which can be supplied to the mixing and weighing apparatus 21 through a valve 31. The wax can be heated to the desired temperature by steam, or water or heated air supplied to the piping 32. Means is provided for supplying a suitable binder to the mixer 21 and consists of a hopper 33 which is provided with a gate 34 for feeding controlled amounts of binder to the mixer 21.

The mixing and weighing apparatus 21 includes a scale 36 so that each component for the mixture to be mixed within the mixer 21 can be carefully weighed into the mixer, either manually or by automatic means (not shown).

The packer 23 in many respects is similar to a bag packer Model DX VP manufactured by the H. L. Stoker Company. This packer is described in detail in my copending application Serial No. 299,760, filed August 5, 1963, now Patent No. 3,240,573.

Means is provided for receiving the bags after they have been filled and are released from the housing assembly, as hereinafter described, and consists of a conveyor 111 which is provided with rollers. As shown in FIG- URE 2, the convey-or 111 is provided with a curved member 114 which causes the filled bags to be turned downwardly so that they are deposited in an upright or vertical position in the conveyor 24.

Operation of the apparatus shown in FIGURE 2 in the manufacture of synthetic fuel logs may now be briefly described as follows. The flame-supporting material is preferably a wax which is heated to the desired temperature in the heater 29. Properly pulverized sawdust, to be used as the filler, is supplied to the hopper 26. A suitable binder is supplied to the hopper 33 and suit-able quantities of all three of these materials are supplied to the mixer 21. The three materials are thoroughly intermixed for the required amount of time in the mixer. Then, a suitable quantity of this mixture is supplied to the hopper 43 of the packer 23. A folded bag is then taken from a bag holder and opened. The mixture is forced into the bag under a substantially uniform predetermined pressure to prevent bridging of the material and to obtain the desired even compaction within the bag. Even compaction is important to keep the log from breaking into segments during burning and to ensure even flames and uniform burning time.

The filled bag drops downwardly into the conveyor 111, after which it is turned by the guide member 114 so that it drops downwardly into the conveyor 24 so that its closed end is on the bottom and its open end is facing upwardly. Thereafter, the bags are moved into a closing station (not shown) wherein the top ends 119 of the bags are folded and sealed with suitable means such as glue or heat-sealing to provide a filled bag which has much the appearance of a fireplace log. For example, such a log can have a diameter of 5 inches and a length of 16 inches. In order to facilitate stacking of the logs, flats 118 are formed on opposite sides of the logs, as shown in FIG- URE 3. FIGURE 3 illustrates the filled bag 116.

As soon as a filled bag has been ejected from the packer, another open bag can be placed upon the spout and the same operation repeated. Thus, it can be seen that bags can be filled in succession rather rapidly with very little delay. The use of the hydraulic control assembly makes it possible to fill all the bags with a uniformly packed mixture. As soon as the mixture in the bag cools, the wax solidifies to provide a synthetic fuel log which is solid at room temperature.

The bag in which the log is formed serves to retain the mixture in the desired shape during the time that the wax-containing mixture is cooling and solidifying. In addition, the bag promotes burning of the log .by being made of a combustible material such as paper. The container increases the logs attractiveness as well and makes a neat and clean package which is easy to handle.

In practice, I prefer to use, as the combustible material of the bag, a paper having a thin layer of polyethylene coated thereon. The polyethylene prevents the oil content of the wax from being absorbed into the paper. If oil saturates the paper, the container is sticky, unsightly and lacks strength. Moreover the polyethylene is flamesupporting and aids in the burning of the log.

In the manufacture of my synthetic fuel logs, numerous parameters must be considered. In addition, the functions of the various components in the mixture must be clearly understood. For example, the sawdust which is utilized serves as a vehicle for sustaining the flame during the burning of the synthetic fuel log, as for example, in a fireplace. Also, the sawdust serves as a heating element. In other words, the sawdust acts as a substrate from which the wax can vaporize and burn. Without the provision of such filler or extender as a substrate, the wax in and of itself would not combust. In order to obtain adequate combustion of the wax, it is necessary that adequate surface area be provided from which vaporization can occur.

There is a wide range of types of sawdust which can be used in making the synthetic fuel log. The sawdust from soft woods such as fir or pine will burn much more readily with a greater and hotter flame but will burn out more quickly. On the other hand, sawdust from certain types of hardwood such as ash or birch will last much longer but will not give a large flame and are slower to ignite initially. For this reason, where hardwoods are to be used, a combination of sawdusts from different types of wood is satisfactory. However, I have found that any type of sawdust will form a satisfactory product. In order to obtain the desired uniformity in the product, it is preferable that the sawdust be pulverized so that any large wood chips and the like are properly sized.

With particles of a relatively uniform size, the interrelated functions of the wood are more easily controlled. Thus, the particles are to be bound together both at low temperatures and at high temperatures. Effective binding requires that the particles be relatively uniform and as small as practicable. On the other hand, very fine sawdust is difiicult to handle and is not satisfactory as a heating element from which to vaporize the wax. In a balance of the opposing considerations, I have found that particles of a size such that they pass a A inch screen are highly satisfactory. While individual particles might exceed A inch in length, it is preferable not to exceed A inch in measuring a cross-section of the chip.

In addition to particle size, the moisture content of the wood is important. Where wood is fully dried to a moisture content of about 6%, larger particles are necessary for effective bonding. That is, fluffy sawdust having little moisture is more diflicult to bind together. It is believed that greener wood is more adaptable to bonding because of reduced surface tension making it more wetable. Wood which is not fully dried may be of smaller particle sizes than dried wood with the same degree of bonding.

A further factor of importance is the temperature and relative humidity at which the sawdust is prepared and mixed. As with dry wood, greater amounts of wax are needed to completely wet and bond the particles on a dry day than on a day of high relative humidity. Temperature variations may require changes in the other process variables. As noted above, I have found that grinding wood to a size such that all particles pass a A inch screen is usually satisfactory for normal variations encountered in practice.

Ambient conditions not only affect the wood grinding process but also affect the pressure of compaction required, the temperature of the mixture in the hopper, etc. Hard woods, as might be expected, require less pressure to compact to a desired density since the wood itself is more dense than softwood. On the other hand, flufiy hardwood is not as easily compacted to a desired volume as fluffy softwood since it is more dense.

Although I have described my synthetic fuel log as utilizing sawdust, other organic material substances can be utilized. The particulate material must be porous to serve as a substrate for the volatile fuel, and should burn completely with a minimum of ash and undesirable smoke or fumes. It should also be capable of being bonded at both low and high temperatures. For example, rice hulls or even shredded paper can-be used to form a satisfactory product.

The wood particles are combustible alone, but they also serve as a substrate for the primary flame-supporting material which is a hydrocarbon. Past efforts at making synthetic logs have used bunker fuel in the logs. Such a fuel, aside from giving off bad odors during burning, was at least potentially explosive. On occasion, conditions existed which caused synthetic logs made with bunker fuel to explode. This gave rise in part to the limited success enjoyed by past synthetic logs. For this reason, a non-explosive fuel is necessary. However, the fuel must be volatile at high temperatures so that it will support flame. Hydrocarbons are preferred since they may be completely burned without odor, ash, or undesirable products of combustion.

As a specific example of a preferred fuel, paraffin wax has been used. By being solid at room temperature, the paraffin wax supplements other binders, yet it is readily vaporized to support flame. No undesirable combustion products are formed, and it is not explosive, as ordinarily defined.

A third critical ingredient of the log, in addition to the combustible particles and fuel, is a low temperature binder. This binder serves to hold the log together at room temperature and temperatures normally encountered in storage. It is desirable to have the lowtemperature binder comustible with a minimum of ash or malodorous products of combustion. Parafiin wax serves this purpose to some extent, but has a melting point too low to provide adequate cohesion under all conditions.

A highly satisfactory low-temperature binder used in practice is microcrystalline wax. This wax has a high enough melting point to provide adequate cohesion under most conditions prior to burning.

Fortunately, a readily available and economical source of both a volatile fuel and a low temperature binder exists in slack wax.

As is well known to those skilled in the art, the slack waxes have not been completely de-oiled. Three primary characteristics can be utilized to describe a slack wax. They are the distillation range, also known as boiling range, the melting point, and the molecular weight. The slack wax can also be characterized by the amount of two general types of waxes (parafiin wax and microcrystalline wax) which it contains.

In analyzing the characteristics of slack wax which makes it particularly desirable for use in my synthetic fuel log, I have found that the microcrystalline waxes in the slack wax provide the cohesive forces that maintain the log as a structural unit, whereas the paraffin waxes provide the desired volatility. The parafiin waxes are a relatively rigid, brittle material and in and of themselves normally would not provide sufficient cohesive forces for the synthetic fuel log.

The microcrystalline waxes suitable for use in my synthetic fuel log can have an initial boiling point ranging from approximately 650 F. -up to and above 1200 F. The melting point of these same microcrystalline waxes can range from approximately 100 F. up to 200 F. The molecuar weight for the microcrystalline waxes can range from 280 to 1200. The percentage of microcrystalline waxes necessary to provide a suitable log having a satisfactory cohesive strength can range from approximately to 50% by weight of the total weight of the slack wax. Above 75%, the volatility of the combustion product is so low that difiiculties occur in maintaining proper combustion of the synthetic fuel log.

At the present time, there are two definitions of slack wax commonly used in the trade. One is whole slack wax which consists of whole wax fractions removed from a lubricating oil refining process without any distillation treatment or de-oiling treatment. The other is partially refined de-oiled fraction from an intermediate stage in refining. The oil content of this fraction would be lower than that of whole slack wax. The oil content of slack wax may thus vary from 10% to 30% by weight. In general, slack wax contains approximately 50% of material boiling above 1000 F. and 50% of material boiling below 1000 F. The initial boiling point is approximately 750 F. However, it is possible that certain slack waxes may include parafiinic type hydrocarbons having a boiling point as low as 550 which would have a melting point of approximately 65 F. Normally, a slack wax having any substantial proportion of such parafiinic type hydrocarbons would be undesirable because of the low melting .point of the same.

From the foregoing, it can be seen that two primary factors must be considered in the utilization of the slack wax. One is cohesiveness and the other is volatility. The cohesiveness is very desirable because it gives the synthetic fuel log structural strength which makes it possible for the log to retain its shape even while it is burning. The volatility of the slack wax is desirable in that it facilitates the starting of the fireplace log and its burning with a good consistent flame. However, the volatility should not be so great that the wax is a liquid at room temperature which would cause the synthetic fuel log to fall apart while it is burning.

The characteristics of a typical slack wax which has proved to be very satisfactory for use in my synthetic fuel log are set forth below.

Melting point, F 150.0 Refractive Index at C. 1.452 Viscosity at 210 F. SSU 60.5 Oil content, percent 19 Molecular weight, average 500 In order to obtain a completely satisfactory synthetic fuel log, it is necesary that the wax be absorbed into the surface of the wood fibers during the time that the synthetic fuel log is 'being manufactured. The degree of absonption must be sufficient so that there is wax available for evaporation from the wood fiber surfaces during burning of the synthetic fuel log and that there be a sufficient amount of wax left over to provide the necesasry cohesive forces to bond the wood fibers together. If too much absorption takes place, there would be insufiicient wax to form the proper bonds. This absorption can be readily controlled during the manufacturing cycle by maintaining proper temperatures during the mixture of the wax and the sawdust by the control of sawdust moisture content.

With the sawdust having a heated temperature of between 80 F. and F., I have found that the temperature of the wax, when it is mixed with the sawdust, can range from approximately F. to 350 F. However, to properly control the sawdust absorption of the wax, it is preferable that the temperature of the wax be kept below 300 F. The time during which the mixture is agitated also determines the amount of absorption of wax 'by the wood fibers. However, I have found that with such temperature, the mixing can range from approximately 5 minutes to 15 minutes, under most situations.

If desired, combustion aids can be provided in the synthetic fuel log in order to increase the speed of combustion. Such combustion aids can be readily introduced in the mixer 21 and incorporated into the product. The types of combustion aids which can be utilized fall into two general categories. One is the type of combustion aid which influences the burning of the carbon deposits formed during the combustion cycle and the other is the type of combustion aid which influences the actual burning of the volatilized hydrocarbons.

The types of combustion aids which influence the ignition temperature of the carbon deposits formed during the cycle of combustion which have been found to be satisfactory are metal organic compounds such as lead naphthanate. Other metal organic compounds can be utilized. However, the organic metal radical selected to carry the metal must 'be one which will give solubility in the wax which is being used. This is desirable because the wax containing the metal will deposit on the wood fibers and will remain on the surface during the combustion cycle and will have its greatest influence on the residual material and will reduce the temperature at which residual carbon will burn by a sufficient degree so that the ash material, instead of being a black carbonaoeous material, is soft, white and nearly completely combusted material.

A combustion aid of the other type is Ferrocene manufactured and sold by Ethyl Corporation which is volatile and will fiow with the wax components and be vaporized, and thus will influence the combustion of the vaporized hydrocarbons whether they come from the sawdust or from the wax.

Relatively small amounts of such combustion aids are required. For example, an amount less than .1% by weight should be more than adequate.

As hereinbefore explained, an additional high temperature binder is provided in order to prevent the synthetic fuel log from breaking up during burning. The microcrystalline waxes in the slack wax, hereinbefore described, serve as a low temperature binder and serve to prevent the synthetic fuel log from falling apart at temperatures ranging up to approximately 160 F. For higher temperatures, the additional binder is utilized to prevent the synthetic fuel 10g from falling apart because the wax tends to reach its melting point prior to being vaporized and, therefore, loses its cohesive qualities, The high temperature binder can be of any suitable type as, for example, a lignin product identified as ammonium lignin sulfonates and wood sugars. One such product is Orzan A manufactured and distributed by the Crown- Zellerbach Corp. Other high temperature binders can be utilized as, for example, Toranil manufactured by the St. Regis Paper Co. In addition, phenol formaldehyde and urea formaldehyde resins probably can be utilized although they have certain obnoxious products of combustion.

In the preferred embodiment, Orzan A is utilized which is in powder form. The mixing operation in step 12 should be such that the Orzan A is thoroughly dispersed throughout the mixture. Orzan A leaves only 1 to 1 /2 ash when burned. Also, on heating to temperatures above 400 F., Orzan A becomes water insoluble and serves as a high temperature binder. It is believed that the presence of reactive phenolic compounds in Orzan A serves to bind the wood particles together at elevated temperatures.

In order to add to the aesthetic features of the synthetic fuel log while it is burning, certain additives can be added to the mixture 21 such as sodium nitrate which will cause sizzling and crackling and a popping during burning to simulate the action of a real wood log. In the place of sodium nitrate, sodium nitrite, ammonium nitrate and potassium nitrate can be utilized if desired.

By way of example, I have found that a synthetic fuel 10g formed of the following ingredients has very desirable characteristics.

Percent by weight Sawdust 42 Slack wax 48 OrzanA 5 Sodium nitrate 5 The sawdust was introduced into the mixer at a heated temperature of approximately F. The Orzan A and sodium nitrate were introduced at an ambient temperature of 60 F. These ingredients were then mixed for a period of 10 minutes, after which the slack wax was sprayed into the mixer at a temperature of approximately 245 F. The product was then mixed for an additional 10 minutes, after which the fuel logs were formed in the packer.

Although the above example represents a preferred composition for my synthetic fuel log, satisfactory logs can be formed with the following ranges for the ingredients.

Percent by weight Sawdust 25 to 75 Wax 25 to 75 Orzan A 2 /2 to 10 The material for the aesthetic qualities can be omitted without affecting the quality of the synthetic fuel log.

Although the compaction of the mixture within the bag affects the burning characteristics of the synthetic fuel log, I have found that it is normally desirable to compact the mixture down to at least half its original size or, in other words, to apply compaction pressures ranging from approximately 400 lbs. per inch to 1000 pounds per square inch. Thus, logs having a density ranging from 30 to 40 lbs. per cubic foot are quite satisfactory.

In practice, it is convenient to seek a log weight of 6% pounds. The general dimensions of the log are 5 inches in diameter and 16 inches in length. By varying pressures, proportions, amounts, etc. to achieve a product weight of 6.25 lbs. reasonably uniform logs may be produced even though the sawdust and other ingredients and operating conditions may vary to some extent.

While the preferred log weight is about 6.25 lbs., a range of from 5 /2 to 7 lbs. per log is satisfactory. The length of the log should be between 12 and 18 inches and 4 to 6 inches in diameter for convenient handling and use.

It is apparent from the foregoing that I have provided a new and improved synthetic fuel log and a method for the manufacture of the same. The synthetic fuel log, because it is provided with an outer covering which is readily combustible, can be readily ignited. A log having a size of approximately 5 inches in diameter and 16 inches in length will burn evenly for over two hours and at the same time giving off a good and consistent flame which virtually surrounds the log and emits a very minimum of objectionable odors and smoke. Because the wax forms a low temperature binder and also because the high temperature binder is utilized, the log will not break up during the burning even though it may be disturbed.

I claim:

1. A synthetic fuel log comprising a compacted mass of particles of sawdust having a wax absorbed thereon and a high temperature binder dispersed throughout the mass between the sawdust particles, said wax including a low temperature binder, the sawdust comprising between 25 to 75% the weight of the mass, the wax comprising between 25 to 75% the weight of the mass and the high temperature binder comprising between 2 /2 and 10% by Weight of the mass.

2. A synthetic fuel log as in claim 1 wherein said mass is in the form of an elongate solid body together with a wrapping of combustible material enclosing the solid body.

3. A synthetic fuel log as in claim 2 wherein said wrapping is formed of a sheet of paper having an oil resistant coating.

4. A synthetic fuel log as in claim 1 wherein said Wax is a slack wax having microcrystalline wax ranging from 20 to 50% by weight.

5. A synthetic fuel log comprising a compacted mass of particles of sawdust having a wax absorbed thereon and a high temperature binder dispersed throughout the mass between the sawdust particles, the wax including a low temperature binder, the sawdust comprising between 25 and 75% by weight of the mass, the wax comprising between 25 and 75 by weight of the mass, and the high temperature binder comprising between 2 and 10% by weight of the mass, said low temperature binder serving to hold the mass together at room temperature and up to an initial burning temperature of approximately 400 F. or less, said high temperature binder by reacting at a temperature of approximately 400 F. and above serving to hold the mass together at temperatures above 400 P. so that the low temperature binder and the high temperature binder in combination serve to hold the mass together to provide a long burning fuel log.

6. A synthetic fuel log as in claim 5 together with a wrapping of combustible material enclosing the mass and serving as a sole means of enclosing the mass.

7. A synthetic fuel log comprising an elongate solid body formed essentially of a mixture of compacted particles of sawdust and wax with the wax being absorbed on the sawdust particles, said wax having constituents serving as a low temperature binder to bind said mixture into a cohesive, unitary mass at room temperature, said sawdust ranging from 25 to 75% by weight of the total weight of the log and said wax ranging from 25 to 75% by weight of the total weight of the log and a high temperature binder comprising over 2 by weight ofthe total weight of the log intimately dispersed in said mixture and serving to hold the log together during the burning of the log.

8. A synthetic fuel log as in claim 7 together with a covering of a combustible relatively impervious sheet-like material enclosing said body and being in intimate con tact with said body and serving as sole means enclosing the body.

9. A synthetic fuel log as in claim 7 wherein the wax is a slack wax of the type having from 20 to 50% microcrystalline waxes by weight which serves as the low temperature binder and wherein the high temperature binder is an ammonium lignin sulfonate and wood sugars.

10. In a method for the manufacture of a synthetic fuel log from sawdust particles and wax including a low temperature binder and a high temperature binder, the steps of causing melted wax to be absorbed on the sawdust particles, mixing said sawdust particles with the wax absorbed thereon with the high temperature binder to provide a moldable plastic mixture, compacting the mixture into an elongate body before the wax has had an opportunity to solidify, and hardening said wax with the low temperature binder therein to solidify and bind the mixture into a cohesive solid body having the desired configuration.

11. A method as in claim 10 wherein the compacting is completed by extruding the mixture into a combustible bag.

12. A method for manufacturing synthetic fuel logs utilizing sawdust particles, a wax having a constituent serving as a low temperature binder and a high temperature binder, the steps of causing melted wax to be absorbed onto the sawdust particles so that the sawdust particles range from 25 to of the total weight of the log, mixing the sawdust particles with the wax absorbed thereon with the high temperature binder to provide a moldable plastic mixture and compacting the mixture into an elongate solid body having the desired configuration.

13. In a method of manufacturing synthetic fuel logs, the steps of pulverizing sawdust to a particle size such that it substantially passes through a ,4 inch screen, heating the sawdust to a temperature of approximately F, introducing the heated sawdust into a mixer, introducing ammonium lignin sulfonate and wood sugars into said mixture at ambient temperature and mixing to evenly distribute the ingredients, spraying slack wax into the mixer at a temperature of approximately 245 E, continuing mixing to evenly distribute all ingredients, compacting the mixture into a combustible container at a pressure between 400 and 1,000 lbs. per square inch, closing the container and permitting the slack wax to solidify, whereby an elongated solid body is formed.

14. In a method for manufacturing synthetic fuel logs, the steps of heating sawdust particles substantially all of which are capable of passing through a inch screen to a temperature above normal room temperature, mixing the sawdust particles with a high temperature binder, spraying molten slack Wax into the sawdust particles and the high temperature binder so that the slack wax is absorbed onto the sawdust particles to form a moldable plastic mixture in which the sawdust comprises from 25 to 75% by weight of the total weight of the log and the wax ranges from 25 to 75% of the total weight of the log and compacting the moldabie plastic mixture into an elongate solid body to provide a log of the desired configuration.

References Cited by the Examiner UNiTED STATES PATENTS 1,106,289 8/1914 Dymond 44-17 1,983,560 12/1934 Palmer 4417 2,107,054 2/1938 Haymond 4441 2,734,365 2/1956 Ferris et a1. 447.5 X 2,789,890 4/1957 Stevens 444l 2,849,300 8/1958 Berman et al. 44-17 X FOREIGN PATENTS 115,645 5/1919 Great Britain. 631,868 11/1949 Great Britain.

DANIEL E. WYMAN, Primary Examiner.

C. F. DEES, Assistant Examiner. 

1. A SYNTHETIC FUEL LOG COMPRISING A COMPACTED MASS OF PARTICLES OF SAWDUST HAVING A WAX ABSORBED THEREON AND A HIGH TEMPERATURE BINDER DISPERSED THROUGHOUT THE MASS BETWEEN THE SAWDUST PARTICLES, SAID WAX INCLUDING A LOW TEMPERATURE BINDER, THE SAWDUST COMPRISING BETWEEN 25 TO 75% THE WEIGHT OF THE MASS, THE WAX COMPRISING BETWEEN 25 TO 75% THE WEIGHT OF THE MASS AND THE HIGH TEMPERATURE BINDER COMPRISING BETWEEN 2 1/2 AND 10% BY WEIGHT OF THE MASS. 